Inside VHS, the difference between HiFI and Linear Audio.

Having operated my own analog videotape editing studio for over 15 years I was required to learn about what I call the functional "technical" aspect of the various videotape formats that I worked with. In this article I will briefly explain the difference between HIFI VHS, Linear Stereo VHS, and Linear Mono VHS and the various tape speeds that can affect the Linear audio channels.

One of the most crucial evaluations that needs to be done when performing a VHS transfer of a VHS videotape to digital in a studio setting is the audio. The Studio Transfer Apecialist has to check both the High Channel, the Linear Audio Channels to see if they are stereo or mono, compare the audio levels between the HIFI and the linear, and listen to the audio levels to determine which set of audio tracks sounds better.

Normally the VHS HIFI (if the VHS Tape had HIFI recorded on it) will sound better. VHS HIFI is in the plus 90 signal to noise ratio, it's really good sound. However, if the manual tracking on the professional machine is not optimally aligned, the HIFI track can start to sound degraded, along with the picture as well. The HIFI audio was actually encoded within the picture part of VHS whereas the linear audio ran alongside the side of the videotape. The Society of Motion Picture Television Engineers has much more in depth technical explanations then what I am giving here in regards to sound.

I am going from my own experiences so its possible I am not 100% correct about the historical order of things but here goes. When VHS first came out audio was linear stereo. While linear stereo had allegedly lower specs than the next great VHS audio, HIFI, Linear Stereo audio was very crisp. The problem was when people recorded in the six hour mode versus the two hour mode the linear stereo audio was very hissy because the videotape speed was running at 1/3 the speed when compared to the 2 hour record mode. At some point Dolby technical was used to reduce the hiss from all linear audio. The VHS Videotape Recorder usually would proudly state that it had Dolby Audio.  

After Linear Stereo HIFI stereo audio was then released. Amazingly, many VHS recorded tapes may have both HIFI stereo and some form of linear audio as well. The linear audio could either be stereo audio, or it could be linear mono. The HIFI audio channels did not need Dolby, only the linear audio tracks did.

If the VHS tape only has mono linear audio, the VHS to Digital Transfer Specialist can also introduce Dolby from an actual professional VHS machine to reduce hiss while also performing a sound equalization adjustment to see if the hiss can be reduced without losing most of the highs. A really good VHS to Digital Studio will have a bypass EQ button so they can flick a switch back and forth between the dolby version with Sound EQ and the  non dolby version with Sound EQ to see which one sounds best.

The practice of being able to instantly flip back and forth between two types of audio adjustments and picture adjustments sets apart a high end VHS to Digital Transfer Studio from others. When some say that any VHS player that plays back your videotape will do when it comes to transferring to digital, that is only partially true. The VHS player may not have either Time Base Stabilization or Time Base Correction which creates a method for syncing the VHS video during the Transfer, and the VHS player may not select the optimal sound track from the VHS tape that it is playing.

There was also a four hour VHS speed mode which ended up being a videotape speed that was never supported in the professional VHS SVHS playback world. My studio can playback either 2 hour or 6 hour speed tapes at extremely high quality, but four hour speed recording is the lone wolf format that whatever is out machine wise can play four hour tapes back at about the same quality. If there was ever a machine that actually played back four hour speed with either Time Base Stabilization, or Time Base Correction, I never found out about it and I was looking back in the 90's for such a machine. 

The primary reason to use a high end studio for a four hour VHS tape is if there was no HIFI recording, only linear audio, and the client wants the audio to be optimized via sound equalization.

As you can see, simply doing a sound quality evaluation and improvement can take anywhere from 15 minutes to an hour, or longer, depending on how long the recording is and if the sound recording parameters changed throughout the recording. The good news is if the videotape is relatively stable then its possible that only one sound evaluation and optimization is necessary. The bad news is if the VHS videotape has significant changes in audio quality throughout the entire tape the audio adjustments can easily take much longer than the picture adjustments.

If you have ever watched your home videos without sound, then turned the sound on, many times the sound adds another layer of intimacy and sentiment to the video. On the other hand, since most people can't afford to have each and every VHS video they own transferred in a supervised setting because of cost, sometimes it may be best to truly focus on a just a couple of tapes that matter the most to you for redoing the VHS transfer to digital in a studio setting.

Contact Alessandro Machi at vhs at Alexlogic.com if you want to book a session in his amazing Analog to Digital Studio. Alessandro's Studio Credits include over 25 IMDB credits and a Los Angeles Emmy. He is also currently ranked top 25 out of 20,000 Lifetime Tongal Ideationists. Mr. Machi also won the prestigious Academy of Television Arts and Sciences Internship Scholarship Award in the Commercials Category many moons ago.